Competing adaptations maintain nonadaptive variation in a wild cricket population

Area of Science:

• Evolutionary biology
• Genetics
• Animal behavior

Background:

• Adaptive evolution in wild populations is driven by interactions between emerging variants.
• The Hawaiian field cricket (Teleogryllus oceanicus) provides a model for studying these interactions.
• Two distinct adaptive phenotypes, curly-wing and flatwing, have emerged in these populations, both conferring protection from parasitoid flies (Ormia ochracea).

Purpose of the Study:

• To investigate the genetic basis of the curly-wing and flatwing phenotypes.
• To understand the evolutionary dynamics of these co-occurring adaptive variants.
• To determine the impact of phenotype co-expression on adaptive fixation.

Main Methods:

• Crosses and genomic/mRNA sequencing to identify genetic underpinnings of curly-wing.
• Reanalysis of existing data for flatwing's X-linked inheritance.
• Population genetics simulations and field observations to model evolutionary trajectories.

Main Results:

• Curly-wing is associated with variation on a single autosome.
• Flatwing inheritance is confirmed as X-linked and single-locus.
• Fitness epistasis between curly-wing and flatwing prevents either phenotype from reaching fixation despite significant fitness benefits.

Conclusions:

• The co-occurrence of alternative adaptive phenotypes can inhibit their fixation in wild populations.
• Fitness epistasis is a significant factor limiting adaptive evolution in sexually reproducing organisms.
• Interactions between emerging adaptive variants may be a more common evolutionary force than previously recognized.